Flash memory devices include a variety of programmable devices such as electrically programmable and electrically erasable/programmable random access memory (EPROM) and (EEPROM) devices. Besides their use to store basic input-output system (BIOS) codes in computers, flash memory devices increasingly gain popularity for use as memory cards or flash cards to store data in electronic products including digital cam corders, digital cameras, and wireless devices.
A typical flash memory device includes a number of memory cells. Each memory cell stores a bit of data in form of a logic 0 bit or logic 1 bit. The flash memory device performs a write operation to store data into the memory cells. To erase the stored data, the flash memory device performs an erase operation to convert the contents of all of the memory cells into logic 1 bits.
A typical flash memory device performs the erase operation in two main steps. In the first step, the flash memory device performs a pre-programming cycle to convert the contents of all memory cells into logic 0 bits. In the second step, the flash memory device performs an erase cycle to convert the contents of all memory cells into logic 1 bits. In a typical flash memory device, some memory cells hold data as logic 1 bits. Therefore, in the typical erase operation, it is not efficient to convert the contents of these memory cells into logic 0 bits in the pre-programming cycle then convert the bits back to logic 1 bits in the erase cycle.
For these and other reasons stated below, and which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need to improve the erase operation of a flash memory device.